Isolation Valve Syngas Gate vs BALL 1

[deepu78]

I have a query regarding Isolation valves in syngas service.
Current Valve size is 16"(400NB)class 600
Temperature 293 deg C
Pressure 35 Bar
Current Valve is a GATE VALVE.

What are the pros and cons of using a BALL VAlVE in the place of above GATE VALVE.

DV

 

[Danlap]

What sort of gate valve are you using?
Syngas is very toxic acute and have some nasty particles within. Hence tightness (minimum to zero leakage) and 'scrapping' capability is critical.
Have tried all kind of 12"-900# valves for syngas 350degC, I would say through conduit gate valve is best suited for this application.

Reasons (all valves below as mentioned we have experienced with):
- wedge gate valve --> easily worn out on sealing area between wedge and seat, due to particles
- trunnion mounted ball valve --> particles stuck on ball and when operated it will scratches ball/seat surfaces; also springs to energize seat against ball are also prone to stuck/damage.
- dual expanding gate valve (with springs connecting both slab/gate)
- dual expanding gate valve (with cam mechanism connecting both slab/gate) --> bottom cavity will be packed with pollution in no time, hence prevent this type to be fully closed. Also prone for only one side of slab which seal and the other falling behind

Through conduit gate:
- cavity in theory is protected
- if equipped with drain/bleed, then this can be additional point of safety measure prior isolating/blind the other side of the valve.
- 'scrapping' capability
- downside: full contact between slab and seat at all position, which lead to higher friction, hence considerable medium to big size actuator is required.

Best regards,
Danlap

 

[LittleInch]

deepu78,

This tells you why your current piping class has all welded gate valves....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[deepu78]

The current valve is a Pressure seal Parallel slide gate valve
see picture below

 

[Danlap]

Seems like Ring-O maybe Safe-O seal valve or copy of it. Easily 30+ years old
Not good:
- Diaphragm (under item 02) and ring seal 20 subject for fatigue due to pressure cycles
- when not fully energized (usually first stage of start-up), this valve have leakage path to outside (see hole next to 21). I wont be stand next to it knowing that Syngas is inside
- when valve fully open, top cavity sooner or later will be filled up with particles. of which will hardened. Browse through conduit gate valve, you'll see the complete difference of cavity 'protected' when it is close, half open and fully open position.

I've reach my free advise limit for today.

Regards,
Danlap

 

[deepu78]